19. Variation and population genetics

Question 1

What does variation mean

Answer 1

The differences in characteristics or phenotypes that exist

Question 2

what is a Phenotype

Answer 2

The expression of the genotype and its interaction with the environment

Question 3

What is a genotype

Answer 3

The genetic constitution of an organism determined by the combinatioon of alleles that an organisation inherits from its parents

Question 4

What is interspecific and intraspecific variation

Answer 4

Interspecific variation occurs between different species.

Intraspecific variation occurs within a species.

Question 5

How is variation due only to Genetic Factors

Answer 5

Certain characteristics of individuals in a population fall into a limited number of distinct forms, with no intermediates
This is due to genetic factors only, where only one or two genes act

Question 6

what does certain characteristics within a population vary only slightly between one individual and another result in

Answer 6

a range of values from one extreme to the other.
Features that vary in this way are often controlled by many different genes (polygenic) and/or are usually also influenced greatly by the environment.

Question 7

What does a genetic variation graph look like

Answer 7

A bell-shape curve
The mean medium mode are all equal

Question 8

What are causes of variation

Answer 8

Environmental
genetic - Meiosis mutaions and random fusion of gametes

Question 8

How doe the genotype and environment link to the phenotype

Answer 8

Genotype + Environment = Phenotype

Question 9

Which method of genetic variation is the only way is asexual organisms

Answer 9

Mutations

Question 10

How is meiosis a source of genetic variation

Answer 10

Meiosis is the formation of gametes
Cells are genetically different
Meiosis is a major causse of intraspecific variation

Question 11

Which two ways doe smeiosis cause genetic variation in gametes

Answer 11

Crossing over
Independent segregration of chromosomes

Question 12

How does random fertilisation of gametes causes variation

Answer 12

Which gamete fuses with which at fertilisation is a random process and this produces new combinations of alleles and the offspring are therefore genetically different from their parents

Question 13

How does mutation cause genetic variation

Answer 13

causes a change in the number or sequence of bases in the DNA of an organism. This produces a change in the characteristics of the organism which can be passed on to cells produced by division of the mutant cell

Question 14

How does the frequency of a mutation occur

Answer 14

the basic mutation rate can be increased by outside factors known as mutagenic agents or mutagens

Question 15

What are mutagenic agents

Answer 15

· High energy ionising radiation. This can disrupt the structure of DNA
· Chemicals

Question 16

What are the types of mutations

Answer 16

Addition/deletion
Substitution
Duplication of bases
Inversion of bases
Translocation of bases

Question 17

How does an addition/deletion mutation cause genetic variation

Answer 17

extra base is added or removed.
This changes all the subsequent triplets after the mutation and a different amino acid sequence is made.
known as a frame shift mutation, as the ‘reading frame’ of the gene changes.
A deleted base near the end of the sequence is likely to have a smaller impact

Question 18

How does a substitution mutation cause genetic variation

Answer 18

One amino acids in the polypeptide could change. impact will depend upon the precise role of original amino acid
The protein may be a different shape and so not function properly. (known as mis-sense mutation).

· base change could result in the formation of a stop codon that marks the end of translation.
The production of the polypeptide would be stopped prematurely. Final protein would have a significantly altered tertiary structure, and so be non-functional. ( known as a nonsense mutation).

· could cause no difference due to the degenerate nature of the genetic code ( known as a silent mutation).

Question 19

What is a duplication of bases

Answer 19

One or more bases are repeated. This produces a frame shift to the right

Question 20

What is an inversion of bases

Answer 20

A group of bases becomes separated from the DNA sequence and rejoin at the same position but in the inverse order
The base sequence of this portion is therefore reversed and affects the amino acid sequence coded for.

Question 21

What is translocation of bases

Answer 21

A group of bases becomes separated from the DNA sequence on one chromosome and becomes inserted into the DNA sequence of the same or a different chromosome.
Translocations often have significant effects on gene expression leading to an abnormal phenotype.

Question 22

What is a population

Answer 22

a group of organisms of the same species living in the same habitat or ecosystem.

Question 23

What is a gene poolq

Answer 23

The sum total of all the alleles of all the gene loci in a population at a particular time.

Question 24

What does hardyweinberg principle allow you to calculate

Answer 24

the proportion of each allele - the allele frequency.

Question 25

What is the hardy-weinberg equation

Answer 25

p2 + 2pq + q2 = 1

p= dominant allele
q= recessive allele
p2 = homozygous dominant genotype
q2 = homozygous recessive genotype
2pq heterozygous genotype

Question 26

What is the hardy-weinberg principle

Answer 26

The frequencies of the alleles of a particular gene in a population will stay constant from generation to generation.

Question 27

What are the conditions in which the hardy-weinberg principle can occur

Answer 27

· The populations must be large
· Mating between individuals must be random.
· No mutations
· All genotypes must be equally likely to reproduce
· There must be no migration into or out of the population

Question 28

What is genetic equilibium

Answer 28

When the hardy-weinberg principle conditions are met and the allele frequency does not change then the population

Question 29

Why is the hardy-weinberg principle never valid

Answer 29

the ideal conditions are never met in real situations

Question 30

what does the fact that a population deviates from the Hardy-Weinberg equilibrium show

Answer 30

that species are constantly in a state of evolutionary flux and it is possible to see to what extent natural selection and evolutionary changes are taking place by how great these deviations are.

Question 31

What is genetic drift

Answer 31

the idea that allele frequencies can change simply due to chance

Question 32

Why may genetic drift occur

Answer 32

beacasue of the founder effect or genetic bottlenecks:

Question 33

What is the founder effect

Answer 33

sometimes happens that a few organisms from a population become isolated from the rest of the population,

Question 34

Waht is genetic bottlenecks

Answer 34

A population said to go through a genetic bottleneck when it is temporarily reduced to a very small number when the majority of individuals are killed. This could be due to a chance event such as disease, volcanic eruption, flooding or hunting.

Question 35

How does the founder effect and genetic bottlenecks affect the allele frequency

Answer 35

the new population size would be much smaller, and therefore the impact of chance on the allele frequencies would be much greater than for the original population
The new population would also show a reduction in genetic diversity due to the loss of some alleles.